⚖️ BMI Calculator

What this BMI calculator does

Enter your height and weight in metric (kg, cm) or imperial (lb, ft/in) and the calculator returns your Body Mass Index, the category it falls in, the weight range that corresponds to a BMI of 18.5–24.9 at your height, and how many kilograms separate you from that range. It runs in your browser, so the numbers you type are not sent anywhere. It is meant for adults aged 18 and over.

The formula

BMI is weight divided by height squared. In metric units that is BMI = kg ÷ m². In imperial units it is BMI = (lb × 703) ÷ in²; the 703 simply converts pounds and inches into the same scale as kilograms and metres.

Worked examples

• 70 kg, 175 cm. 1.75 × 1.75 = 3.0625. 70 ÷ 3.0625 = 22.9, which is in the normal range.
• 85 kg, 178 cm. 1.78 × 1.78 = 3.1684. 85 ÷ 3.1684 = 26.8, which is in the overweight range. At 178 cm, a BMI of 18.5–24.9 corresponds to roughly 58.6–78.9 kg, so this person is about 6 kg above the top of that range.
• 160 lb, 5 ft 6 in. 5 ft 6 in is 66 in. 160 × 703 = 112,480, and 66 × 66 = 4,356. 112,480 ÷ 4,356 = 25.8, also overweight, but only just over the 25 line.

BMI categories

The World Health Organization classifies adult BMI like this:

• Below 18.5: underweight
• 18.5 to 24.9: normal weight
• 25.0 to 29.9: overweight
• 30.0 to 34.9: obesity, class I
• 35.0 to 39.9: obesity, class II
• 40.0 and above: obesity, class III

These are population screening bands, not medical boundaries. Someone at 24.8 is not meaningfully healthier than someone at 25.2.

Where BMI misleads

• Muscle. BMI cannot tell muscle from fat. A strength athlete can land in "overweight" with low body fat.
• Where fat is stored. Fat around the waist carries more health risk than fat on the hips and thighs, and two people with the same BMI can differ a lot here. Waist circumference is a useful second check.
• Ethnic background. A WHO expert consultation published in The Lancet in 2004 found that people of Asian descent can carry higher risk of type 2 diabetes and heart disease at lower BMI values, and suggested additional action points at 23.0 and 27.5. South Asian and Arab communities, including many residents of the UAE, may want to discuss their own targets with a doctor rather than rely on the standard 25 line.
• Age. Older adults lose muscle, so the same BMI can hide more body fat than it does in a young adult.
• Children and teens. Under 20, BMI is read against age- and sex-specific percentile charts, not the adult bands above. Do not use this calculator for a child.
• Pregnancy. BMI is not a valid measure during pregnancy.

Using the result sensibly

Treat BMI as a starting point for a conversation, not a verdict. If your result is outside the normal range, the more useful next steps are to check your waist measurement, think about recent changes in your weight, and talk to a doctor or dietitian, particularly if you have a family history of diabetes or heart disease. If you are in the normal range, BMI says nothing about your fitness, diet or sleep, so it is not a reason to stop looking after those. To go further, the body fat calculator estimates composition rather than just weight for height, and the TDEE calculator estimates how many calories you burn in a day.

This tool is for general information and does not replace medical advice.

Sources

Category bands: World Health Organization, "Obesity: preventing and managing the global epidemic" (WHO Technical Report Series 894, 2000). Asian cut-off points: WHO Expert Consultation, "Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies," The Lancet, 2004. BMI for children: US Centers for Disease Control and Prevention, BMI-for-age growth charts.